APTOPIX Explosion Nashville

This undated image posted on social media by the FBI shows Anthony Quinn Warner. Federal officials now turn to exploring the monumental task of piecing together the motive behind the Christmas Day explosion that severely damaged dozens of buildings and injured three in downtown Nashville, Tenn. While officials have named 63-year-old Warner as the man behind the mysterious explosion in which he was killed, the motive has remained elusive. (Courtesy of FBI via AP)